Solutions containing hydrogen peroxide have heretofore been proposed for use in various processes involving the dissolution of metals and metal oxides. Exemplary of these are processes involving pickling, etching, cleaning, chemical brightening or polishing, and the like. Typical disclosures of pickling solutions are found in G.B. Patent Application No. 2,014,552A directed to a solution of hydrogen peroxide and a mineral acid with a saccharin stabilizer and G.B. Pat. No. 1,499,918, and its equivalent U.S. Pat. No. 4,022,703, directed to a solution of hydrogen peroxide and sulfuric acid with an 8-hydroxyquinoline stabilizer. Typical disclosures of etching solutions are found in G.B. Pat. No. 1,474,294, directed to hydrogen peroxide in an aqueous fluoride solution with tetrazoliumn as an inhibitor, G.B. Pat. No. 1,295,954 directed to an alkaline solution of hydrogen peroxide containing a metal ion complexor and a stabilizer, and G.B. Pat. No. 962,335 directed to a solution of hydrogen peroxide and ammonium fluoride. A typical disclosure of a metal cleaner is found in G.B. Pat. No. 1,407,269 directed to the use of ferrous sulfate, hydrogen peroxide or nitric acid, sulfuric acid and a bifluoride. Typical disclosures of chemical brightening or polishing solutions are found in G.B. Pat. No. 1,209,016, directed to the use of hydrogen peroxide, ammonium bifluoride, oxalic acid and sulfamic acid and in G.B. Pat. No. 1,056,670 directed to the use of hydrogen peroxide and hydrofluoric acid.
In many of the above-mentioned disclosures, the need for a stabilizer for the hydrogen peroxide is recognized. In addition to the recognition in these patents, other disclosures have recognized the general need for stabilization of hydrogen peroxide solutions. Typical of these are French Pat. No. 998,486, directed to the use of oxyquinoline compounds, such as the sulfate, and U.S. Pat. No. 3,053,632, directed to the use of 2-alkyl substituted 8-hydroxyquinolines.
With the growth of the printed circuitboard industry in recent years, there has been an increasing need for compositions which will strip or remove solder from other metal substrates, such as copper. In the manufacture of printed circuitboards, tin or tin-lead solders are frequently applied to copper components of the circuitboard, such as the terminal tabs. It is then necessary to remove the solder from the copper substrate so that it can be plated with a more noble metal, such as gold. Additionally, there are frequent occurrences of mis-soldering which make it necessary to remove the improperly applied solder from the copper substrate in order to recover the copper plated printed circuit substrates for resoldering. In view of the high production rates for the printed circuitboards, rapid removal of the solder composition is essential. Such removal must, however, be accomplished without significant attack on the copper substrate.
Attempts to utilize the various hydrogen peroxide based metal treating compositions as described above to effect the solder stripping have, generally, not been successful. When used to strip tin and tin/lead alloy solders from copper substrates with these compositions, the stripping rates have been too slow and/or the attack on the copper substrates has been too great.
Accordingly, attempts have been made to develop hydrogen peroxide based solutions which are particularly adapted for solder stripping. In U.S. Pat. No. 3,841,905, for example, there is described a solder stripping composition of hydrogen peroxide and ammonium bifluoride. U.S. Pat. No. 3,926,699, which was reissued as Reissue No. 29181, describes a hydrogen peroxide and ammonium bifluoride solder stripping composition which contains, as a stabilizer, a combination of Dequest and triisopropanol amine. In G.B. Pat. No. 976,167, there is described a solder stripping composition of hydrogen peroxide and fluoboric acid. Another solder stripping composition is described in G.B. Patent Application No. 2,074,103A, which composition is made up of hydrogen peroxide, ammonium bifluoride, trichloroacidic acid and a polyacrylamide. In G.B. Pat. No. 1,446,816 or its equivalent U.S. Pat. No. 3,986,970, yet another solder stripper composition is described which is comprised of hydrogen peroxide, an acid, a source of fluoride ions and a stabilizer for the hydrogen peroxide. Among suitable stabilizers disclosed in the patent is 8-oxyquinoline. Although these compositions have been used with varying degrees of success, they have generally not been able to provide the high rates of solder stripping, without attack on the copper substrates, which are presently required in the manufacture of printed circuitboards.
It is, therefore, an object of the present invention to provide an improved solder stripping composition and process.
A further object of the present invention is to provide an improved solder stripping composition and process characterized by high solder stripping rates without significant attack on the metal substrate, such as copper.
These and other objects will become apparent to those skilled in the art from the description of the invention which follows.